To configure ISDN settings:

1.Open Network Connections
2.Select dial-up connection that uses ISDN, click Change settings of this connection.
3.On the General tab, in Connect using, click the ISDN device, then click Configure.
4.In the ISDN Configure dialog box, do one or both of the following:
-In Line type, click the line type you want to use. Line types are listed from highest to lowest quality.
-If you want to start negotiation with the line type you selected, and then negotiate with a lower-quality line type, select the Negotiate line type.

Here you will find information on how to configure a leased line.